code: def test_at(self):
      pdf = self.pdf
      psdf = self.psdf
      # Create the equivalent of pdf.loc[3] as a Koalas Series
      # This is necessary because .loc[n] does not currently work with Koalas DataFrames (#383)
      test_series = ps.Series([3, 6], index=["a", "b"], name="3")
  
      # Assert invalided signatures raise TypeError
      with self.assertRaises(
          TypeError,
          msg="Use DataFrame.at like .at[row_index, column_name]",
      ):
          psdf.at[3]
      with self.assertRaises(
          TypeError,
          msg="Use DataFrame.at like .at[row_index, column_name]",
      ):
          psdf.at[
              "ab"
          ]  # 'ab' is of length 2 but str type instead of tuple
      with self.assertRaises(
          TypeError, msg="Use Series.at like .at[column_name]"
      ):
          test_series.at[3, "b"]
  
      # Assert .at for DataFrames
      self.assertEqual(psdf.at[3, "b"], 6)
      self.assertEqual(psdf.at[3, "b"], pdf.at[3, "b"])
      self.assert_eq(psdf.at[9, "b"], np.array([0, 0, 0]))
      self.assert_eq(psdf.at[9, "b"], pdf.at[9, "b"])
  
      # Assert .at for Series
      self.assertEqual(test_series.at["b"], 6)
      self.assertEqual(test_series.at["b"], pdf.loc[3].at["b"])
  
      # Assert multi-character indices
      self.assertEqual(
          ps.Series([0, 1], index=["ab", "cd"]).at["ab"],
          pd.Series([0, 1], index=["ab", "cd"]).at["ab"],
      )
  
      # Assert invalid column or index names result in a KeyError like with pandas
      with self.assertRaises(KeyError, msg="x"):
          psdf.at[3, "x"]
      with self.assertRaises(KeyError, msg=99):
          psdf.at[99, "b"]
  
      with self.assertRaises(ValueError):
          psdf.at[(3, 6), "b"]
      with self.assertRaises(KeyError):
          psdf.at[3, ("x", "b")]
  
      # Assert setting values fails
      with self.assertRaises(TypeError):
          psdf.at[3, "b"] = 10
  
      # non-string column names
      pdf = self.pdf2
      psdf = self.psdf2
  
      # Assert .at for DataFrames
      self.assertEqual(psdf.at[3, 1], 6)
      self.assertEqual(psdf.at[3, 1], pdf.at[3, 1])
      self.assert_eq(psdf.at[9, 1], np.array([0, 0, 0]))
      self.assert_eq(psdf.at[9, 1], pdf.at[9, 1])
  
imports: import datetime
  import unittest
  import numpy
  import pandas
  from pyspark import pandas
  from pyspark.pandas.exceptions import SparkPandasNotImplementedError
  from pyspark.testing.pandasutils import PandasOnSparkTestCase, compare_both
  from pyspark.testing.sqlutils import SQLTestUtils
label_desc: Use image node_id 5 for calling the IndexingAdvMixin obj's underlying member method code with example usage: obj.test_at() without return types